I would like to consider my music library eclectic but most of what I listen to is hip-hop/bass dominant tracks. Which IEM between the gr07 and ba200 is best with those tracks?

It would go with your preference for balance of low to mid bass. You already ordered so don't second guess yourself. Wait until you get it, burn it in for just a few hours, nothing drastic like 300, and have a listen to a few tracks. If you think its great, then great, if you feel its lacking something, PM me and I'll tell you if the BA200 has what you think is lacking.

It really depends on the type of double flange - e.g. not all medium double-flanges are the same size. It really varies quite a bit by manufacturer.

well looks like you no longer have the HA-FX40 but I will ask anyway. One guy bought these tips http://www.meelec.com/MEElectronics_Eartips_p/ts1-df-50-cl.htm for his FX40 and he said they are too big for his ears, so I would like to know which double flange tips has similar size with fx40 stock tips, also any tip for choosing tips size?

well looks like you no longer have the HA-FX40 but I will ask anyway. One guy bought these tips http://www.meelec.com/MEElectronics_Eartips_p/ts1-df-50-cl.htm for his FX40 and he said they are too big for his ears, so I would like to know which double flange tips has similar size with fx40 stock tips, also any tip for choosing tips size?

Is it a big difference between the VSonic GR07 BE, JVC FXT90 and the Westone UM2? I'm currently owner of the UM2 and I'm looking after the GR07 BE or/and the FXT 90 to replace them. Is it a downgrade on SQ or not? Thank you